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WW1 Thornycroft restoration

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Many thanks for all of your thoughts. I am pretty sure that I don't need the hot air inlet as modern fuels are so much more volatile. However, I will keep that one up my sleeve for the time being. I have been doing other things today whilst I mull it over but I have investigated the timing and this is what I have found. Taking 'valve opening' or 'closing' as the point at which the tappets contact or part then, at the moment:

Inlet opens at TDC

Inlet closes 34° after BDC

Exhaust opens 32° before BDC

Exhaust closes 5° after TDC

I don't have a Thornycroft timing chart and my Dennis one is in Leicester. However, these figures don't look right to me at all. The adjustment I have is to move the camshafts by numbers of teeth. The crank pinion has 29 teeth so each tooth represents just over 12°. I should value your advice please.

In the meantime, I have connected the throttle pedal to the linkage. This was another puzzle as, although a copy of an original, my pedal seems to be 1 1/2" too long. I have drilled a new hole for the ball joint, a bit closer to the pivot and it all works well.

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We also assembled the tailboard.

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The planks are aligned with tongues in the grooves and held together by the bolts in the hinge straps.

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Dad painted the underside of the hinges and put a single top coat on the planks earlier in the week so that we won't get a line of primer as the planks move with time.

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Dad then finished up by top-coating the inside whilst I drilled and fitted the foot brake pivot casting.

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I shall continue with the footbrake mechanism until we have worked out what to do with the camshafts!

Steve   :) 

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This is the timing diagram for the 4 litre Dennis sidevalve engine of the 1930’s.

 

98A09AD9-529E-4379-A3FE-3715E7CABE72.png

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Hi Steve and family! As many others have said already and will say: well done! It is quite an achievement to bring a 100 year engine back to life. If it is only the valve timing that needs to be adjusted, well that is a minor thing compared to the other work you have done. I would say too that the valve timing is a bit far off, especially on the inlet side. My guess is to advance the inlet by 24° and the outlet by 12° and see what happens. Inlet open at TDC is way too late. An impulse magneto will definitely help, not sure if you need a choke though when everything is adjusted as it should. Is there a way to prime the engine? You are quite right about the modern fuels. I had to change the nozzle on the Peugeot from 145 to 125 because it smoked too much. 

Best regards

Marcel 

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Steve,

I can't find valve timing details that directly compare to the Thornycroft engine but I could easily believe that the figures that you quote above are correct. A more modern engine would have more inlet opening both before and after but certainly not 12 degrees earlier unless it is supercharged. Similarly you don't see much later exhaust closing on older engines. Engines that I have worked on with wrong valve timing (admitedly with a single camshaft) just run badly, they don't idle well but refuse to rev up and die. I think it is carburettor ! At least it goes. I would want to put it in gear and see it move for the first time in many many years. Well done for getting this far without a heart atack.

David

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When you compare the Thorny with the Dennis, the valve timing looks very similar. The duration of the Thorny exhaust period is shorter but the difference is located equally with respect to the Dennis exhaust timing. Is the problem really valve timing after all?

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Timing diagram from a  1920’s 4 cylinder SV engine of 3 litre capacity. Still not radically different.

 

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Here is yet another timing diagramme for an early Australian made engine. It is just another example, I guess.

On the question of volatility of modern fuels, when unleaded petrol was mandated here in the late 80's, it would not run vintage engines satisfactorily, continuously fouling spark plugs. It was 91RON, which is still the main fuel here (the worst in the world!). We have to use premium grades 95 or 98RON for our hobby machines, at significant cost premium. It is generally held they are LESS volatile, being formulated for fuel injection rather than evaporative use via carburettors.

Ian

Timing diagram.pdf

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Just realised the pdf file is a bit useless, so here it is as a jpg.

ian

Timing diagram.jpg

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Thank you very much for that gentlemen. What I have really doesn't look very different from these charts. As you mentioned, Cel, my initial thought was that the inlet was too late but it seems very similar to these. I feel inclined to leave it alone for the moment and have another run first as it has still only started once. After it stiffened up, I couldn't swing it properly again!

The stiffening up is a bit odd. I set the ring gaps very carefully according to the instructions on the packet and during the first run, it didn't really get very hot so I would be surprised if it was them. We shall see.

Thanks for your help. I'll keep you posted!

Steve    :)

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Hopefully the engine has freed up now it is cold again. If not there is the possibility that something has 'picked up' which would be depressing. It would be worth checking that the oil is still clear.  There is no way that you could finish the wearing surfaces as finely as a modern production line so it is bound to need a lot of running in. But well done for getting this far.

David

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Steve. 

I agree that the valve timing looks near enough vs the period data to suggest that its correct. 

Stiffening up is a concern. Will it turn now its cold?. I think with it idling youd have noticed a change in engine note and it would have got very hot had the bores gone tight. Realistically just idling id be very surprised if it picked up.

Is it simply that it has bedded in a bit, and now has built more compression? Can you turn it minus the plugs?

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14 minutes ago, 8_10 Brass Cleaner said:

Steve. 

I agree that the valve timing looks near enough vs the period data to suggest that its correct. 

Stiffening up is a concern. Will it turn now its cold?. I think with it idling youd have noticed a change in engine note and it would have got very hot had the bores gone tight. Realistically just idling id be very surprised if it picked up.

Is it simply that it has bedded in a bit, and now has built more compression? Can you turn it minus the plugs?

Steve can reply properly later on, Hedd, but it has loosened again now that it is cold. We plan to run it again this afternoon -"as -is" - and see what happens this time.

Tony

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Tony

The way it idles suggests that timing wise, be it valve or ignition is in more or less the right shop.

Opening the throttle can only be doing something unwanted to the mixture.

A simple check for mixture is to use your hand over the intake to choke the air as the throttle is opened. If you can get more revs by throttling the air, then it points to under fuelling, assuming the carb is the correct size. It wont rev like it should but it will rev more. another similar test, put petrol in a hand pump bottle that will spray a mist. Introduce some into the intake as the throttle is opened. Does this increase the revs? 

 

 

 

 

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Also check for air leaks, sucking in air will also cause the engine to cut out. 

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Posted (edited)

Congratulations to you all on getting the engine running.

Re; Tight engine

I am supprised to see that they still make 'Running In Oil' which should help ease a tight engine. Morris Lubricants supply what they call 'Classic Running In Oil' available in stright grades 30sae and 40sae.

Re; Acceleration problem

I seem to remember that there is a spring controlled govenor on the camshaft, is this coming in too soon and stopping the engine accelerating; weak or soft springs prehaps.

John

Edited by Barney

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Started the day by making up the pivot pin for the foot brake. Only managed one decent photo though.DSCN5536.JPG.b28afddb783cd0630b313c7fd912c813.JPG

All the linkage is a pain and the main pedal rod goes through the seat box so will do some more of that tomorrow.

This afternoon, we had a visitor and took the opportunity to run the engine again. Using the choke board, it is very easy to start so that is one blessing! It idled nicely but again, just didn't want to accelerate. We had a couple of good bangs and flashes back through the carburettor in the process. As it warmed up, it stiffened and after one of my throttle opening tests, it died. It wasn't so stiff this time although we could hear something tight, so I managed to swing it again for another go. It ran again but eventually died whilst I was messing. Whilst we thought about it some more, David, our guest, had a look at the mag and asked me to advance it. This I did but he saw no movement as we found that one of my joints in the linkage had failed and although I was pushing the lever, nothing was happening. I started it up again and advanced the magneto manually. What a difference! We could now open the throttle and rev the engine. Not sure that we are completely there but it is all looking much more promising. Also, after ten minutes, we switched it off and I tried to turn it again. It was stiff but nothing like as bad as the first time and I could have started it again so that looks promising too.

I have just come in after fixing the advance linkage and will concentrate on the brakes and footstep tomorrow. I have also found an oil leak which needs attention. Always something!

Steve    :)

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46 minutes ago, Barney said:

Re; Acceleration problem

I seem to remember that there is a spring controlled govenor on the camshaft, is this coming in too soon and stopping the engine accelerating; weak or soft springs prehaps.

Hi John.

Yes, there is a governor but although the linkage is all there and connected, I did not make a butterfly for it. At least that is one variable we can eliminate!

Steve    :)

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13 minutes ago, Old Bill said:

Hi John.

Yes, there is a governor but although the linkage is all there and connected, I did not make a butterfly for it. At least that is one variable we can eliminate!

Steve    :)

Sounds like you are winning.

The fact that it is freeing off a little is good too. What do you think sounded tight?

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A search through the box of Thornycroft manuals shows no M4 engine  guides. The handbooks are all for the later engines. The scanned copies below are for the HB4 and the BB4 engines. Overall the valve timing is basically the same, the only difference I can see is the distance measurements relating to the different flywheel diameters.

 Hope this can be of help.

 Doug W

 

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Thanks Doug. They do look very similar to what I have got so I feel inclined to leave it alone for the time being. It is nice to have confirmation.

Steve :)

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Team Gosling,

I don't have access to valve timing diagrams, I'm not qualified to offer advice, but I can say thank you. It's like reading a  good book you just can't put down, I can't wait to turn the next page. Congratulations on getting the engine running, I hope that's giving you a lift that will see you and the Thornycroft on the start line for the London to Brighton - Good luck

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Posted (edited)
12 hours ago, Prague1996 said:

Team Gosling,

. It's like reading a  good book you just can't put down, I can't wait to turn the next page.

Glad you are enjoying it. I only wish I knew how the book was going to end as it could still go either way!

Another interesting day. It started off with great excitement as the differential spider arrived. Barry very kindly arranged for the spline to be cut by wire erosion and then sent it on.

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I had to go underneath and see if it would fit and it is perfect. I shall take it back to Leicester and drill the bolt holes ready for my next visit when we plan to fit it and make up the prop shaft. Thanks Barry.

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We filled the gearbox.

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Then I noticed the oil level gauge. The aluminium tube which sits on top of the float was right at the top when it was only 3/4 yesterday.

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This was distinctly concerning so we drained the oil and removed about a gallon of water in the process.

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Now we are puzzling as to where it has come from. There is no head gasket and we leak tested the blocks before fitting them. The only thing I can think of is that the persistent drip from the top water castings is falling onto the flat top surface of the crank case and then running in underneath the cam followers which are only clamped to the top surface. Hopefully, when we cure the water hose leaks, the problem will go away. Fingers are crossed but it has cost us a sump full of oil at least.

On a happier note, I moved onto the footbrake mechanism. I found a spring to use as the pedal return and also cut and threaded the pull rods.

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The return springs on the shoes are not quite right so I have ordered up some new ones. Once they arrive, I can set it up completely and tick that job off.

Finally, we made a start on the footstep. This consists simply of a board bolted to two heavy bent steel brackets. The main puzzle was how to bend them but the trusty press soon made short work of them.

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I have since trimmed them to length and drilled for bolts. We will put it together tomorrow morning and then Dad can clean up and paint them. After that, we are onto the wing brackets. These are going to be hard as they are bent and welded to look like forgings. Lots of hours there and I only have two days left. We are getting very close to the wire!

Steve    :)

Edited by Old Bill

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Steve.

See attached photo please.

What is the purpose of the dingle dangle? Something to do with damping vibration perhaps, but it seems too small?

Regards

Doug

Thorny.JPG

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It's been a while sice I checked this thread. A lot of work being finished since last time I was here. As usual well done guys!!

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10 minutes ago, dgrev said:

What is the purpose of the dingle dangle? Something to do with damping vibration perhaps, but it seems too small?

That is part of the brake adjustment. The rod has left and right hand threads and can be rotated to take up wear. The weight just stops it rotating in use and gives the driver something to grip to tighten the brakes. I have not seen the idea anywhere else.

Steve   :)

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